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zram: remove max_comp_streams internals

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Remove the internal part of max_comp_streams interface, since we
switched to per-cpu streams.  We will keep RW max_comp_streams attr
around, because:

a) we may (silently) switch back to idle compression streams list and
   don't want to disturb user space

b) max_comp_streams attr must wait for the next 'lay off cycle'; we
   give user space 2 years to adjust before we remove/downgrade the attr,
   and there are already several attrs scheduled for removal in 4.11, so
   it's too late for max_comp_streams.

This slightly change a user visible behaviour:

- First, reading from max_comp_stream file now will always return the
  number of online CPUs.

- Second, writing to max_comp_stream will not take any effect.

Link: http://lkml.kernel.org/r/20160503165546.25201-1-sergey.senozhatsky@gmail.com
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Sergey Senozhatsky
2016-05-20 16:59:59 -07:00
committed by Linus Torvalds
parent d34f615720
commit 43209ea2d1
4 changed files with 18 additions and 58 deletions
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Documentation/blockdev/zram.txt
+7 -18
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@@ -59,27 +59,16 @@ num_devices parameter is optional and tells zram how many devices should be
pre-created. Default: 1.
2) Set max number of compression streams
Compression backend may use up to max_comp_streams compression streams,
thus allowing up to max_comp_streams concurrent compression operations.
By default, compression backend uses single compression stream.
Regardless the value passed to this attribute, ZRAM will always
allocate multiple compression streams - one per online CPUs - thus
allowing several concurrent compression operations. The number of
allocated compression streams goes down when some of the CPUs
become offline. There is no single-compression-stream mode anymore,
unless you are running a UP system or has only 1 CPU online.
Examples:
#show max compression streams number
To find out how many streams are currently available:
cat /sys/block/zram0/max_comp_streams
#set max compression streams number to 3
echo 3 > /sys/block/zram0/max_comp_streams
Note:
In order to enable compression backend's multi stream support max_comp_streams
must be initially set to desired concurrency level before ZRAM device
initialisation. Once the device initialised as a single stream compression
backend (max_comp_streams equals to 1), you will see error if you try to change
the value of max_comp_streams because single stream compression backend
implemented as a special case by lock overhead issue and does not support
dynamic max_comp_streams. Only multi stream backend supports dynamic
max_comp_streams adjustment.
3) Select compression algorithm
Using comp_algorithm device attribute one can see available and
currently selected (shown in square brackets) compression algorithms,